Marine Fisheries Depletion

Marine fisheries will only continue to become more important given the ever-growing population of humanity.  Marine fisheries currently employ about 200 million people worldwide and account for nearly $70 billion in revenues annually; about 19% of the animal protein consumed by humanity is in the form of fish.  Approximately 22% of global marine fisheries are currently overexploited.  Though a slightly vague term, “overexploitation” attempts to identify species of fishes which are being exploited to such an extent that they cannot reproductively rebound from having been harvested.  Other categories include: fully to heavily exploited, moderately exploited, underexploited, and recovering.  Given the overwhelming importance of fisheries to a growing human population and its economy, this evidence of 22% of fisheries being overexploited is quite startling.

Humans have experienced and felt the pain of depleted fisheries before.  In the 1940s, sardine stocks in the Pacific Ocean off the coasts of Japan and California collapsed; a similar event occurred in 1972 off the coasts of Peru and Chile.  While these collapses had tremendous effects on the areas dependent on fishing for jobs (a topic explored in Cannery Row by John Steinbeck), they were of global importance too, as sardines, anchovies, and related species have consisted of 7 of the worlds top 10 harvested fishes.  The collapse of anchovy populations in 1972 should have been one of the first warning signs that fisheries were harvesting at unsustainable rates; however, the collapse was blamed on an El Nino event, though there was strong evidence that over fishing was a cause.  Blaming the collapse on environmental events, however, allowed fishing to continue as usual and the effects of the collapsing fish population were felt in fisheries in the North Atlantic.

Despite those collapses and the clear ways in which they were mismanaged, problems with over fishing have persisted through the decades. While most studies agree that global fisheries began to decline in productivity sometime around the 1980’s, evidence suggests that it dates back a bit further to the late 1960’s and early 70’s.  In the 1980’s, this trend accelerated with a collapse of cod stocks off the coast of Northeastern North America in the Atlantic. Regardless of the exact time fisheries as a global whole began to fall out, the earth is currently in something of a dire position regarding fish stocks.

As industrial fishers (as well as recreational fisheries, something I will discuss shortly) often target larger fish, they have drastically reduced predatory fish populations to approximately 10% of pre-industrial levels.  While the effects of this on global fish stocks are incalculable, the other half of their study showed that industrial fisheries reduced community biomass by 80% within fifteen years of exploitation.  However, as fishing often begins before studies do, it is possible that community biomass declined even more.

Furthermore, recreational fishing has had dramatic effects on fish stocks as well.  Previously, scientists believed that recreational fishing was too unsubstantial to have any strong impacts on fish populations (they believed it accounted for less than 2% of fish harvesting).  However, 23% of harvests of “populations of concern,” which includes fish that either have been over-fished or are experiencing over-fishing.  Recreational fishers actually equal industrial fisheries in their exploitation of summer flounder, scup, and red snapper.

Recreational fishers are also often subject to rather insufficient regulation.  Most recreational fishers, if regulated at all, are regulated in regard to “bag” and “size limits.”  These types of limits result in regulatory discards which can have numerous unforeseen consequences.  Regulatory discards result in mortality rates which are higher than estimates would suggest due to dead fish being thrown back into the water; they also have sublethal effects such as stunted growth or inhibited reproduction as a result of damage from having been hooked and then discarded.  There is currently no way of quantifying these types of interactions and their effects.  Furthermore, as recreational fishers are even more biased towards exploitation of top-level predators than commercial fishers, their effects on fish stocks are likely disproportionate to industrial effects because removing top-level predators has drastic effects on community biomass.

Industrial fishing can, however, have extremely devastating consequences aside from physically removing fish from their habitats, including dredging, trawling, long-hauling, and igniting explosives.  These practices kill sessile organisms which provide structural habitat on the relatively featureless ocean bottom.  This has dramatic effects on benthic biogenic communities which in turn can result in incalculable ramifications on marine communities as a whole.  These indirect effects may have greater consequences than the direct effects of fish removal (for more information, see Botsford, L., Castilla, J., Peterson, C. 1997. The Management of Fisheries and Marine Ecosystems.  Science.  Vol. 277 no. 5325: 509-515).

The Problems

Now, equipped with an understanding of the dismal state of global fisheries and the effects of industrial fishing, I ask: what should be done to solve the problem.  The human population is only continuing to grow; fish will certainly play a role in feeding and employing that population.  However, we would be jumping the gun if we were to immediately delve into mitigation efforts.  While the reasons for individual species collapses are complex and numerous, we can classify the causes into two major groups: (1) knowledge as to how communities will react by tweaking one component of an ecosystem is limited at best and monitoring of oceanic fish populations is similarly limited and (2) socio-political pressure to keep fisheries yields up each year results in prioritizing short term economic goals while ignoring the finite nature of natural resources.

Shortcomings of Current Scientific Models

Even when stock abundances remain high, the effects of size-selective fishing reduce genetic diversity, average age, and average sizes at a given age.  These sorts of manipulations in fish populations can have unforeseen effects on community structure.  The reduction of average size and age structures reduces biomass which, in turn, alters community structure.  This leads to the primary problem with contemporary science and monitoring global fish stocks: most fisheries observe fisheries as single-species stock assessments. That is to say that in a fishery that focuses on a given species, assessments as to the health of that population and the appropriate harvesting levels focus solely on that species and often ignore the community and habitat structures which usually regulate those fish populations.  These species are discussed in terms of “Maximum Sustained Yields,” focusing on individual fisheries and what is required to keep them running.

This single-species assessment approach is, quite frankly, inappropriate given the global nature of fish populations.  Clearly, the approach is not holistic enough and ignores too many relevant components. The “Maximum Sustained Yield” model “is conducive neither to global predictions nor the collaborative development of long-term scenarios.” (For more information, see Pauly, D., Alder, J., Bennet, E., Christensen, V. Tyedmers, P., Watson, R. 2003. The Future of Fisheries.  Science. 302: 1359-1361).  As was the case with anchovy collapses as well as the massive decline in top-level predatory fish worldwide, a more global approach is necessary in order to deal with fishery declines.

Perhaps an analysis of trophic structures could provide a better method of observing fish population hardiness.  Most marine trophic levels range from 3.0 to 4.5.  These numbers pertain to the amount of steps involved in the food chain (e.g. sardines feeding on zooplankton are fed on by large cod, etc).  Global fisheries have experienced a .05-.10 decline in trophic levels per decade in the past few decades.  Of course, this decline in trophic levels implies a slow but certain removal of long-lived, large predatory fish.

However, a trophic structure analysis also has its weaknesses.  Food web descriptions and energy flow models often represent the environment as being static and do not anticipate changes in populations that occasionally occur naturally, such as the large scale regime shift in 1976 which saw a dramatic shift from a shrimp-dominated northern Gulf of Alaska to a fish dominated gulf.

Political shortcomings

Couple our inability to interpret data effectively with our inability to adequately sample world oceans and you arrive at a rather troublesome conclusion.  Unfortunately, stock levels at which recruitment to a given population will rapidly decline is not known until it happens.  Similarly, the subsequent behavior of predators and competitors is unknown.  These scientific uncertainties make regulation particularly difficult.

While, ecologically, it would be wonderful to apply the precautionary principle to fisheries exploitation, it is at odds with the economic need to increase production.  Indeed, since the point at which stock levels will begin to decline is almost impossible to determine, it is difficult to give sufficient scientific evidence that a population should be either harvested less or sometimes not at all.  When there is any question as to the results of increased harvests, political pressure to increase output invariably wins out.  Much of this political pressure, however, is derived from an even greater ignorance than that inherent in simple single-species assessments.  Politicians seem inclined to believe, that, “somehow, the oceans will yield what we need- just because we need it.”

The “there will always be more” approach is deeply entrenched in the western mentality, going back to the nineteenth century notion that marine fishes were inexhaustible (perhaps not such a nineteenth century notion, but one ever-present in man cultures- at least from Locke).  The rationale of choice today among policy makers is that we have explored so little of the ocean that there must be so much more productivity in the deep sea.

Although we have not adequately explored the world’s oceans, we do have a basic understanding that this assumption is false.  Consider this: less than 7% of the planet’s oceans are shallower than 200m and not all of that is accessible (primarily because of ice cover).  That 7%, the continental shelves, house over 90% of global fish catches.  The open oceans simply do not possess the nutrients to support a substantial amount of productivity.  These open ocean zones are similar to deserts.  Politicians’ assumptions that the gigantic ocean will always have more for us to harvest would be similar to believing that once we had farmed all arable land around oases in the rest of the land in the Sahara would be ripe for growing.  Of course, this approach completely ignores the fact that nothing substantial will be able to grow throughout most of the Sahara any time soon.

Politics further complicates sustainable harvesting of fisheries in that it is too deterministic and self-serving to the point of fault.  An interesting example of this can be seen at the end of the 20th century in United States coastal zones.  With the decrease in fisheries yields of the 1970’s and 1980’s, the American government became increasingly concerned that foreign involvement in stock harvesting was causing a decline in their fisheries output.  As a result, they enacted 16 U.S.C. § 1801, commonly known as the Magnuson Act, which effectively eliminated foreign competition by removing foreign fleets from US waters.  After about twenty years, however, it became clear that foreign involvement had nothing to do with declines in fisheries outputs and amendments were made to emphasize a reduction of fishing pressure.  This course of events goes to show how reticent politicians are to actually regulate fish extraction.  (This is not to suggest that the Magnuson act was either a bad law or an inappropriate law; rather, to suggest that it was an incomplete law).  Indeed, depletion was seen as the effect of someone else’s meddling with American resources rather than a product of unsustainable exploitation.  As a result, unsustainable exploitation continued without any sort of substantial regulation for another twenty years.

Where To Go?

Given the problems and the obstacles to conservation, I turn to current attempts at mitigation that seem to be promising.  However, I think I should preface this discussion with a few points.  Conservation attempts and even attempts at increasing yields can only do so much.  As long as we approach fisheries as deposits that can supply humanity with whatever sort of yields we need, we will never have a sustainable fishery industry.  A holistic approach which values the complex community structures and the finite nature of marine fishes is imperative.  Furthermore, the precautionary principle should begin to override the desires for increased yields and reckless exploitation of populations to which the effects of exploitation are unknown.  Yes, critics will argue that that is all well and good, but there are still mouths to be fed and jobs to be had.  Of course, no one is denying the importance of high fish yields regarding both feeding and employing hundreds of millions or even billions of people.  The point is that the continuation of the current fishing model will only result in a long term decrease in fisheries yields along with an increase in habitat destruction which will in turn result in more hungry people and less jobs.

That being said, there are some exciting efforts at conservation across the planet right now.  Perhaps the most important and notable conservation attempt has been in the realm of Marine Protected Areas (MPAs). These areas, which are often designated as no-take reserves, can actually result in a net increase in fisheries production.  That is to say, given a marine area X, if one were to make a portion of X into a no-fishing reserve and leave the remainder open to fishing, the amount of fish extracted from the remaining area will often be greater in the long run than it would have been had the entire area X been harvested.

More than simply increasing net productivity, MPAs increase biodiversity and create better habitats which affect every trophic level and can feed populations outside of the reserves.  Furthermore, these areas help to combat the homogenization of populations in regard to size structures, age structures, and genetic diversity.

A notable example of where these MPAs have been affective is in Fiji where after five years of banned fishing, clams reached sizes bigger than had been seen in generations and their abundance increased 13 fold.  These MPAs also improved seagrass habitat which brought about the return of species which had disappeared from the area years before, such as seahares and stingrays.

In New Zealand, egg production of lobster at deep water sites increased by 9% for each year of protection and snapper productivity was 18 times greater in protected areas than fished areas.

As we can see from these examples, MPAs have positive effects on the species of concern as well as other species which can have numerous benefits.  Many scientists argue that approximately 20% of shallow world oceans must be turned into marine reserves by 2020 to reverse the trend of global fish depletion.  Currently, about .01% of the world’s oceans are protected.

The dramatic difference between where MPAs should be compared to where they are leads me to the conclusion that, barring any dramatic changes in the way humanity views itself in relation to the planet’s natural resources, a sustainable fishing industry is unlikely to ever come to fruition.  Present trends, despite being informed of inevitable fishery demise, imply an expansion of fishing into deeper waters with greater impacts on biodiversity and fish habitats and, despite all that, a continued decline in global catches.  Clearly, this necessitates a dramatic shift in the way fisheries are managed.  While scientific advances will be able to help, more holistic perspectives along with the protection of vast amounts of shallow oceans are imperative to any continuing success of fisheries.  While accruing support for these sorts of efforts in the short term may be difficult, in the long run they will result in increased, sustainable fisheries yields, something extremely important for an ever-growing human population.

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